1. Field of the Invention
This invention relates in general to a method for manufacturing a series-connected thin-film solar cell module made of crystalline silicon.
2. Description of the Prior Art
So as to exploit regenerable energy sources, specifically solar energy, it is necessary to develop efficient solar cells and solar modules which are inexpensive and efficient. Solar cells are already available in low power applications for example, for driving electronic clocks or pocket calculators, but the efficient generation of power by solar energy in general power applications has not been satisfactorily accomplished because of high cost of materials and manufacturing costs.
It is thus necessary to develop highly efficient large area stable low cost solar cells or modules for photovoltic energy generating for substantial amounts of power. Solar cells of crystalline silicon are preferred because of their high efficiency in energy conversion.
Current solar modules of crystalline silicon are disclosed, for example, in a report by M. I. Smokler in the Proceedings of the Sixth European Solar Energy Conference, London, 1985, pages 370 through 376 which describes individual solar cells of about 0.4 mm through 0.5 mm thickness that each have an area of about 10 cm.times.10 cm. The separately produced individual cells must first be joined together to form larger solar modules and must be soldered to each other using metallic bands in a complicated manner for electrical interconnection. Series and/or parallel connection of the individual cells are possible.
A significant increase in the size of the crystalline individual cells is not possible because excessively high photocurrents occur under illumination as, for example, AM1 light which is a light that has a spectrum and intensity that corresponds to solar radiation at the terrestrial equator at sea level when the sun is in the overhead position and such high currents cannot be removed by the finger-shaped contacts in a satisfactory manner. Adhesion problems arise with regard to the contacts on the silicon which reduce the performance of the cell, particularly when large temperature differences occur in the day/night cycle which goes from hot to cold. By contrast, reinforcing the contact leads causes additional light shadowing and, thus, also results in losses in performance.
So as to manipulate the individual silicon substrates, they are far thicker about 0.4 mm so as to obtain mechanical stability, which thickness is far greater than would be required to obtain complete light absorption. For example, a crystalline silicon layer already absorbs 90% of the light of AM 1.5 illumination when the layer thickness is 100 .mu.m. The known crystalline silicon solar modules thus have previously been limited to use for small and thick silicon layers.